The invention relates to a process and an arrangement for pneumatic false-twist spinning having at least one pneumatic false-twisting nozzle arranged between a drafting roller device and a withdrawal device.
In the case of pneumatic false-twist spinning, a false twist is forced on a sliver in the false twisting nozzle, which sliver has been drawn in a drafting roller device to a desired yarn size. After the passage through the false-twisting nozzle, this false twist that was forced onto the sliver opens up again, in which case, however, fibers located in the edge area that are anchored with only one end in the sliver, remain wound around this fiber connection. In order to carry out the false-twist spinning, a variety of arrangements have become known, exemplary disclosures being contained in the following patent applications: European Patent applications (EP) Nos. A 57 876, A 94 802 and A 121 602; Japanese applications (JP) Nos. OS 52-55 737 and OS 59-112 035, and German Published Unexamined Patent Applications (DE-OS) Nos. 20 42 387, 23 30 410, 24 24 769, 27 41 690, 33 25 699, and 35 19 887. However, all these known arrangements are unsatisfactory for a practical application at least to the extent that their realm of application is very limited.
The invention is based on the objective of opening up a larger area of application to pneumatic false-twist spinning and in particular, making it applicable also to longer and coarser fibers.
This objective is achieved according to the invention by at least partially reducing the effective twist that was applied to the sliver by the false-twisting nozzle, and by the spreading-away of fiber ends from the sliver in at least the area that has a reduced twist.
The invention is based on the basic idea that, for successful false-twist spinning, it should be endeavored to spread away from the sliver as many fiber ends as possible that will then be available for a winding-around. In this case it should mainly also be endeavored that the spread-away fiber ends that are available for a winding-around are distributed as evenly as possible over the length of the sliver because only then an even distribution of strength is possible that leads to a high overall yarn stability. The known arrangements meet these requirements only insufficiently. Although it is known from European Patent Application (EP) No. A 57 876 to connect means in front of the false-twisting nozzle that have the purpose of promoting a spreading-away of fiber ends, in this arrangement, the twist that is applied to the sliver is reversed into these means. The sliver in this area forms a yarn balloon, so that the contact with the means for the spreading-away of the fiber ends is uneven and the fiber ends can be spread-away only in a corespondingly uneven way. It is also known from European Patent Application (EP) No. A 94 802; and German Published Unexamined Patent Application (DE-OS) No. 33 25 699) to avoid or to reduce the reversing of the false twist that was applied to the sliver by the false-twisting nozzle by means of a special development of the inlet area of the false-twisting nozzle. Although as a result, the possibility of the spreading-away of fiber ends in the area located in front is improved, the spreading-away itself is still largely left to chance, so that also by means of this arrangement, no uniform yarn can be produced, particularly in the case of longer fiber lengths.
In a further development of certain preferred embodiments of the invention, it is provided that the sliver is only prestrengthened by the false-twist spinning and after passing through the withdrawal device is finished by a subsequent spinning or twisting process. In the case of this development, the produced yarn receives from the false-twist spinning only a part of the strength required for its further use. The remaining part is generated by a subsequent processing of the only prestrengthened sliver. In this case, it is important that the areas of the false-twist spinning and of the subsequent further treatment of the prestrengthened sliver are separated from one another by the withdrawal device, so that particularly a reactive effect of the subsequent treatment on the area of the false-twist spinning is avoided. It was found that in the case of this type of development, the requirements are lower that must be established with respect to the uniformity of the spread-away fiber ends. If the strengthening of the sliver that can be achieved by the false-twist nozzle is utilized only partly, a clearly more uniform yarn is obtained, also where there is no completely even distribution of the spread-away fiber ends relative to the length.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.